Re: [Qemu-devel] [PATCH] rtl8139: honor RxOverflow flag in can_receive method

["Fernando Luis Vázquez Cao" <fernando@oss.ntt.co.jp>]

(2012年01月31日 13:12), Igor Kovalenko wrote:
> 2012/1/30 Fernando Luis Vázquez Cao<fernando@oss.ntt.co.jp>:
>> Some drivers (Linux' 8139too among them) rely on the NIC injecting an interrupt
>> in the event of a receive buffer overflow and, accordingly, set the RxOverflow
>> bit in the interrupt mask. Unfortunately rtl8139's can_receive method ignores
>> the RxOverflow flag, which may lead to a situation where rtl8139 stops receiving
>> packets (can_receive returns 0) when the receive buffer becomes full.
>>
>> If the driver eventually read from the receive buffer or reset the card the
>> emulator could recover from this situation. However some implementations only
>> do this upon receiving an interrupt with either RxOK or RxOverflow set in the
>> ISR; interrupt that will never come because QEMU's flow control mechanisms would
>> prevent rtl8139 from receiving any packet.
>>
>> Letting packets go through when the overflow interrupt is enabled makes the
>> QEMU emulator compliant to the spec and solves the problem.
>>
>> This patch should fix a relatively common (in our experience) network stall
>> observed when running enterprise distros with rtl8139 as the NIC; in some cases
>> the 8139too device driver gets loaded and when under heavy load the network
>> eventually stops working.
>>
>> Reported-by: Hayato Kakuta<kakuta.hayato@oss.ntt.co.jp>
>> Tested-by: Hayato Kakuta<kakuta.hayato@oss.ntt.co.jp>
>> Signed-off-by: Fernando Luis Vazquez Cao<fernando@oss.ntt.co.jp>
>> ---
>>
>> diff -urNp qemu-kvm-orig/hw/rtl8139.c qemu-kvm/hw/rtl8139.c
>> --- qemu-kvm-orig/hw/rtl8139.c  2012-01-12 20:55:27.000000000 +0900
>> +++ qemu-kvm/hw/rtl8139.c       2012-01-18 17:20:12.000000000 +0900
>> @@ -824,7 +824,7 @@ static int rtl8139_can_receive(VLANClien
>>      } else {
>>          avail = MOD2(s->RxBufferSize + s->RxBufPtr - s->RxBufAddr,
>>                       s->RxBufferSize);
>> -        return (avail == 0 || avail>= 1514);
>> +        return (avail == 0 || avail>= 1514 || (s->IntrMask&  RxOverflow));
>>      }
>>   }
>>
>>
>>
> Acked-by: Igor Kovalenko<igor.v.kovalenko@gmail.com>

Thank you for the review and the ack, Igor.

Anthony, could you pick up this patch?

Regards,
Fernando